This chapter is from the book

This chapter is from the book

The Adobe Portable Document Format (PDF) is the native file format of the
Adobe® Acrobat® family of products. The goal of these
products is to enable users to exchange and view electronic documents easily and
reliably, independently of the environment in which they were created. PDF
relies on the same imaging model as the PostScript® page description
language to describe text and graphics in a device-independent and
resolution-independent manner. To improve performance for interactive viewing,
PDF defines a more structured format than that used by most PostScript language
programs. PDF also includes objects, such as annotations and hypertext links,
that are not part of the page itself but are useful for interactive viewing and
document interchange.

1.1 About This Book

This book provides a description of the PDF file format and is intended
primarily for application developers wishing to develop PDF producer
applications that create PDF files directly. It also contains enough information
to allow developers to write PDF consumer applications that read existing
PDF files and interpret or modify their contents.

Although the PDF specification is independent of any particular software
implementation, some PDF features are best explained by describing the way they
are processed by a typical application program. In such cases, this book uses
the Adobe Acrobat family of PDF viewer applications as its model. (The
prototypical viewer is the fully capable Acrobat product, not the limited
Acrobat Reader product.) Similarly, Appendix C discusses some implementation
limits in the _Acrobat viewer applications, even though these limits are not
part of the file format itself. To provide guidance to implementors of PDF
producer and consumer applications, compatibility and implementation notes in
Appendix H describe the behavior of Acrobat viewer applications when they
encounter newer features they do not understand, as well as areas in which the
Acrobat products diverge from the specification presented in this book.

This third edition of the PDF Reference describes version 1.4 of PDF.
(See implementation note 1 in Appendix H.) Throughout the book, information
specific to particular versions of PDF is marked as suchfor example, with
indicators like (PDF 1.3) or (PDF 1.4). Features so marked may be
new in the indicated version or may have been substantially redefined in that
version. Features designated (PDF 1.0) have generally been superseded in
later versions; unless otherwise stated, features identified as specific to
other versions are understood to be available in later versions as well. (PDF
viewer applications designed for a specific PDF version generally ignore newer
features they do not recognize; implementation notes in Appendix H point out
exceptions.)

The rest of the book is organized as follows:

Chapter 2, "Overview," briefly introduces the overall
architecture of PDF and the design considerations behind it, compares it with
the PostScript language, and describes the underlying imaging model that they
share.

Chapter 3, "Syntax," presents the syntax of PDF at the object,
file, and document level. It sets the stage for subsequent chapters, which
describe how that information is interpreted as page descriptions, interactive
navigational aids, and application-level logical structure.

Chapter 4, "Graphics," describes the graphics operators used to
describe the appearance of pages in a PDF document.

Chapter 5, "Text," discusses PDF's special facilities for
presenting text in the form of character shapes, or glyphs, defined by
fonts.

Chapter 6, "Rendering," considers how device-independent
content descriptions are matched to the characteristics of a particular output
device.

Chapter 7, "Transparency," discusses the operation of the
transparent imaging model, introduced in PDF 1.4, in which objects can be
painted with varying degrees of opacity, allowing the previous contents of the
page to show through.

Chapter 8, "Interactive Features," describes those features of
PDF that allow a user to interact with a document on the screen, using the mouse
and keyboard.

Chapter 9, "Document Interchange," shows how PDF documents can
incorporate higher-level information that is useful for the interchange of
documents among applications.

The appendices contain useful tables and other auxiliary information.

Appendix A, "Operator Summary," lists all the operators used in
describing the visual content of a PDF document.

Appendix B, "Operators in Type 4 Functions," summarizes the
PostScript operators that can be used in PostScript calculator functions, which
contain code written in a small subset of the PostScript language.

Appendix D, "Character Sets and Encodings," lists the character
sets and encodings that are assumed to be predefined in any PDF viewer
application.

Appendix E, "PDF Name Registry," discusses a registry,
maintained for developers by Adobe Systems, that contains private names and
formats used by PDF producers or Acrobat plug-in extensions.

Appendix F, "Linearized PDF," describes a special form of PDF
file organization designed to work efficiently in network environments.

Appendix G, "Example PDF Files," presents several examples
showing the structure of actual PDF files, ranging from one containing a minimal
one-page document to one showing how the structure of a PDF file evolves over
the course of several revisions.

Appendix H, "Compatibility and Implementation Notes," provides
details on the behavior of Acrobat viewer applications and describes how viewer
applications should handle PDF files containing features that they do not
recognize.

A color plate section provides illustrations of some of PDF's
color-related features. References in the text of the form "see Plate
1" refer to the contents of this section.

The book concludes with a Bibliography and an Index.

The enclosed CD-ROM contains the entire text of this book in PDF form.